New study estimates frequency of volcanic eruptions

Holidaymakers concerned about fresh volcanic eruptions causing flight-disrupting ash clouds might be reassured by a study setting out the first reliable estimates of their frequency.

While the University
of Leeds-led research suggests that ash clouds are more common over northern
Europe than previously thought, it puts the average gap between them at about
44 years.

It also reveals
that these types of ash clouds have about a 20 per cent chance of occurring in
northern Europe in any one decade.

Reliable estimates of the frequency of volcanic ash events could help airlines, insurance companies and the public mitigate the losses and disruption caused by ash clouds in the future.

Dr Liz Watson, School of Geography

Lead author Dr Liz
Watson, from the School of Geography at Leeds, said: Reliable estimates of the
frequency of volcanic ash events could help airlines, insurance companies and
the travelling public mitigate the economic losses and disruption caused by ash
clouds in the future.

The work began
soon after 2010s explosive eruption of Icelandic volcano Eyjafjallajökull, which caused more than 10 million air
passengers to be stranded and cost the European economy an estimated £4
billion.

A team of
researchers, which included academics from the universities of St Andrews and
South Florida, compared records of volcanic ash fallout (also known as tephra) during
the last 1,000 years.

Focusing on northern
Europe, which is downwind of Iceland, one of the worlds most active volcanic regions, they examined samples taken from peatlands and lake beds in mainland northern Europe, Great Britain, Ireland and the Faroe Islands, alongside previously
existing samples taken from other sites across northern Europe.

The samples 
cores up to seven metres long  were taken from peat and lake sediment where geological
records are particularly well preserved.

Using electron microscopy
and chemical analysis, the team identified tiny shards of preserved volcanic
ash, called cryptotephra - about the width of a human hair - which enabled them
to pinpoint at what point volcanic ash clouds had spread across the continent.

For many of the
occurrences, the researchers were also able to match sample data to historical records
or to existing geological data which charted specific eruptions.

The work found evidence of 84 ash clouds during
the last 7,000 years, most of which could be traced to eruptions from Icelandic
volcanoes.

More incidences of volcanic ash are recorded over the past 1,000
years, because evidence is better preserved and historical records are more
complete, leading the team to estimate an average recurrence of 44 years.

Co-author Dr Graeme Swindles is Associate Professor of Earth System Dynamics
in the School of Geography at Leeds.

He said: In 2010, when Eyjafjallajökull erupted, people
were really shocked  it seemed to come completely out of the blue, but the
eruption of Grímsvötn, the following year, was an extraordinary coincidence.

Although it is possible that ash clouds can occur on an annual basis, the
average return interval for the last 1,000 years is around 44 years.

The last time volcanic ash clouds affected
northern Europe before the recent event was in 1947, 69 years ago  but aviation
was much less intense at that time and it simply didnt have the same sort of
impact.

Our research shows that, over thousands of years,
these sorts of incidents are not that rare  but people wondering how likely it
is that the 2010 chaos will be repeated in the next few years can feel somewhat
reassured.

The researchers also
looked at the intensity of the eruptions responsible for producing volcanic ash
clouds.

They found that volcanic activity likely to produce ashfall in northern
Europe would typically measure four or above on the internationally-recognised
Volcanic Explosivity Index (VEI).

But in cases where that calculation can be made early on, it will
give a good indication of the likelihood of volcanic ash causing a major
problem.

The 2010
eruption cost billions in terms of lost revenues and there was an effect on the
global economy, so the work weve been able to do to quantify the risk will be
of interest to insurance companies trying to make sense of the potential for
future air traffic disruptions.

Further information

The main image above shows Icelandic volcano Eyjafjallajökull on 29 March 2010. The satellite image shows the volcano's eruption from space, on 17 April (Credit: NASA/MODIS Rapid Response Team)